Our previous immunohistochemical and biochemical studies of cerebral microvessels and cerebrovascular endothelial cultures showed the presence of phenylethanolamine-N-methyltransferase (PNMT) activity in both tissues. Since these extraneuronal tissues contain a catecholamine synthesizing enzyme which is responsible for conversion of norepinephrine to epinephrine, we extended these studies to determine whether vascular PNMT is indeed capable of producing epinephrine from norepinephrine. For this purpose a direct assay of endothelial epinephrine formed from norepinephrine was determined by using high pressure liquid chromatography. These studies, which are still in progress, have shown that the cultured cerebrovascular endothelium (2nd-4th generation) derived from dissociated cerebral microvascular fractions (obtained from rats) are capable of converting norepinephrine to epinephrine.